Biodegradation of biphenyl in a solid–liquid two-phase partitioning bioreactor

Biphenyl was successfully degraded by Burkholderia xenovorans LB400, initially described as Pseudomonas sp. LB400, in a solid–liquid two-phase partitioning bioreactor (TPPB). Solid–liquid TPPBs are comprised of an aqueous, cell containing phase, and a solid polymeric phase that partitions toxic and/or poorly soluble substrates (in this case biphenyl) based on maintaining a thermodynamic equilibrium. The employed polymer was Hytrel™, a thermoplastic polyester elastomer. The surface area available for mass transfer of biphenyl was limiting and resulted in mass transfer limited growth, as demonstrated experimentally by employing two different geometric shapes (cylinders with different aspect ratios) of the polymer phase with different specific surface area, while keeping all other parameters constant. The linear microbial growth rates were substantially higher when more polymer surface area was provided.The mass transfer coefficient of biphenyl from Hytrel™ to water was measured under experimental conditions, which allowed predicting the release rate based on the biphenyl concentration gradient. The partitioning behaviour of biphenyl between Hytrel™ and culture medium was measured as well, which allowed the development of a simple mechanistic model describing microbial growth based on known microbial properties in combination with substrate delivery from the solid polymer phase. The model was capable of describing the experimental data well and can be used to predict degradation rates for other geometric shapes of a solid delivery phase such as sheets or rods, which might be of operational advantage in various applications of TPPBs to the controlled uptake and release of other recalcitrant molecules.